The present invention relates to a four-piece solid golf ball having excellent flight performance and good shot feel at the time of hitting. More particularly, it relates to a four-piece solid golf ball having high launch angle.
Many types of golf balls are commercially selling, but they are typically classified into thread wound golf balls and solid golf balls. The solid golf balls which are mainly commercially selling are two-piece golf balls, which consists of a solid core of molded rubber material and a cover of thermoplastic resin (e.g. ionomer resin) covering on the solid core. The two-piece solid golf ball has such a simple structure, but has long flight performance and good durability. The two-piece solid golf ball is generally approved or employed by many golfers, especially amateur golfers. On the other hand, it is problem that the two-piece solid golf ball has hard and poor shot feel at the time of hitting.
In order to solve the problem, various golf balls such as a three-piece solid golf ball comprising two-layer core or two-layer cover, a four-piece solid golf ball comprising two-layer core and two-layer cover, three-layer core or three-layer cover and the like have been proposed (Japanese Patent Kokai Publication Nos. 336618/1996, 56848/1997, 248351/1997, 266959/1997, 127818/1998, 127819/1998 and the like).
Japanese Patent Kokai Publication Nos. 336618/1996 and 56848/1997 suggest a multi-piece solid golf ball having at least four layers, which comprises a core having at least two layers, and a two-layer cover composed of an inner cover and outer cover. However, in the both golf balls, one of the two-layer cover is made harder and therefore the resulting golf ball has poor shot feel.
Japanese Patent Kokai Publication No. 248351/1997 suggests a multi-piece solid golf ball having at least four layers, which comprises a core, and a cover having at least three layers composed of an inmost layer cover, at least one layer of intermediate layer cover, and an outmost layer cover. However, since one of the intermediate layers is made harder than the inmost layer cover and outmost layer cover, that is, the intermediate layer cover is harder than the outmost layer cover, the shot feel of the resulting golf ball is poor as described in the above.
Japanese Patent Kokai Publication Nos. 266959/1997, 127818/1998 and 127819/1998 suggest a four-piece solid golf ball which comprises a cover and a three-layer core composed of an inner layer, an intermediate layer and an outer layer. However, since the golf balls do not have a structure that an outer portion is harder and an inner portion is softer, the golf ball is not effectively deformed and a launch angle is small, which reduces a flight distance.
These multi-piece golf balls, when compared with the two-piece golf ball, have better shot feel while maintaining excellent flight performance, because the golf balls can have a various of hardness distribution. However, the golf balls, when compared with the thread wound golf ball, have hard and poor shot feel when hitting by a driver or an iron club at a low head speed.
A main object of the present invention is to provide a four-piece solid golf ball having long flight distance by accomplishing high launch angle and low spin amount at the time of hitting, while maintaining good shot feel when hitting by a driver and an iron club at a low head speed.
According to the present invention, the object described above has been accomplished by employing a four-layer structure which comprises a core, an intermediate layer, an outer layer and a cover to form a four-piece solid golf ball, and adjusting a surface hardness of the core, and a hardness difference between the surface of the core and the intermediate layer and a hardness difference between the intermediate layer and the outer layer to specified ranges. The present invention thus provides a four-piece solid golf ball having long flight distance by accomplishing high launch angle, while maintaining good shot feel when hitting by a driver and an iron club at a low head speed. In other words, a deformation amount of the golf ball on impact can be optimized and energy loss because of large deformation amount of the golf ball can be restrained by adjusting hardness distribution of the golf ball so as to increase the hardness from the center point to surface of the golf ball in order, thereby providing a four-piece solid golf ball having excellent flight performance by accomplishing high launch angle when hitting by a driver and an iron club.